1. Field of the Invention
The present invention relates to headgear assemblies, and, in particular, to headgear assemblies used in a respiratory support system to securely position gas delivery masks on a patient.
2. Description of the Related Art
There are numerous situations where it is necessary or desirable to deliver a flow of breathing gas, non-invasively, to the airway of a patient, i.e., without intubating the patient or surgically inserting a tracheostomy tube in their trachea. For example, it is known to ventilate a patient using a technique known as non-invasive ventilation. It is also known to deliver continuous positive airway pressure (CPAP) or variable airway pressure support system such as the BiPAP® device registered to RIC Investments, Inc., or an auto-titration pressure support system which varies with the patient's respiratory cycle or a monitored condition of the patient, to treat a medical disorder, such as sleep apnea syndrome, obstructive sleep apnea (OSA), congestive heart failure, stroke, Cheynes-Stokes respiration, diabetes, etc. In fact, pressure support therapies continue to be found to be of benefit in other medical disorders. Non-invasive ventilation and pressure support therapies involve the placement of a patient interface device, which is typically a nasal or nasal/oral mask, on the face of the patient to interface the ventilator or pressure support device with the airway of the patient, so that a flow of breathing gas can be delivered from the pressure/flow generating device to the airway of the patient.
Because such patient interface devices are typically worn for an extended period of time, two competing concerns must be balanced for effective treatment: comfort and seal integrity. When providing CPAP or other positive pressure therapy to treat OSA, the patient normally wears the patient interface device all night long while he or she sleeps. On one hand, in order to be effective in this application the patient interface device must be as comfortable as possible, otherwise patient compliance will be low thus defeating potential treatment effectiveness. Most patients find a loose fitting mask more comfortable than one that this cinched down tightly on their face. On the other hand, the patient interface must be tightened adequately to provide an airtight seal and prevent the patient interface from becoming misaligned. To further complicate matters, human facial geometry is rather complex about the patient's mouth and nose. This region includes rapidly varying contours. Moreover, the thickness of the soft tissue also varies from region to region about this region of the patient's face. The cheeks tend to be a region with thick soft tissue while the region about the patient's nose tends to have little soft tissue resulting in a comparatively hard region. In addition to these broad generalities, each patient's face is unique, thereby further complicating attempts to create a mask that is comfortable and effective for a wide variety of patients. What is comfortable and effective for one patient may prove to be entirely unsuitable for another.
Typically patient interface devices include a shell or support that is often rigid in construction that supports a mask cushion, mouthpiece, or nasal cannula. The cushion is usually formed from a deformable elastomeric material and directly contacts the patient. To form an airtight seal with the patient, the cushion deforms about the patient's facial contours. The patient interface is held in place by a headgear assembly that includes straps that are wrapped around the patient's head and cinched down to draw the interface firmly against the face of the user. One such headgear assembly exemplary of the art is described in U.S. Patent Application Publication No. US 2002/0117177 (“the '177 reference”). This reference discloses a nasal mask that is held in place by a pair of straps: an upper strap across the patient's forehead region and a second strap extending from the patient's nasal region. The straps are joined together at a coupling member and held in place by a rear webbing portion.
Although this device may operate adequately for its intended purpose, it has several drawbacks as well. For instance, in order to secure the mask on the user's face, the straps and webbing pull the mask inward. The amount of force needed to secure the mask in place far exceeds the amount of force needed to create an airtight seal. Doing so, concentrates a large amount of stress on the region about the patient's nose and mouth. Secondly, the amount of force needed to prevent the patient interface from becoming misaligned far exceeds the amount of force needed to create an airtight seal.
Finally, these patient interfaces have straps that encircle the patient's head. As a result, a force is exerted about the patient's head that squeeze the sides inwardly as the straps circumnavigate the rounded surface of the patient's head.
Another headgear assembly is described in U.S. Pat. No. 6,516,802 (“the '802 patent”) that overcomes some of the above noted disadvantages. Rather than using straps that extend around the patient's head, this reference discloses a mounting member that is looped over the top of the patient's head along the sagittal suture and has a pad below the occipital bone. The pad creates a force to draw the mask into the patient's face.
Headgear assemblies constructed in accordance with the teachings of the '802 patent overcome some of the disadvantages found in the art. Unlike the '177 reference, this device does not extend about the sides of the patient's head. Instead this device loops over the top of the patient's head along the sagittal bone. These headgear assemblies hold the device in place by drawing the cushion inward to hold the patient interface in place thereby, as in the '177 reference, they still concentrate the headgear retaining forces through the mask. Secondly, these headgear assemblies still circumnavigate the patient's head along a substantially curved path following the contours of the patient's head. Furthermore, the use of a single mounting member looped over the patient's head provides even less stability than in the '177 reference. The headgear assembly disclosed in the '802 patent is even more likely to be misaligned if bumped.
In order to overcome some of the disadvantages of the above described headgear assemblies, a headgear assembly was suggested in U.S. patent application Ser. No. 10/918,832 (assigned to the assignee of the present invention and hereby incorporated by reference in its entirety) (“the '832 application”). The patient interface disclosed in this reference includes a mask secured to a headgear by a coupling member. The headgear is adjustable and has a forehead strap, a cross strap, and a rear strap or webbing. The patient interface described in this pending application enhances comfort and provides a superior seal. Rather than securing the patient interface in place by applying a force acting through the mask, this headgear assembly separates the headgear assembly retention from the mask seal. The headgear assembly is secured to the patient's head regardless of the force needed to create an adequate air seal between the patient interface and the patient's face. In fact, the headgear could be worn without even attaching a patient interface. By separating these two functions, the headgear may be appropriately tightened to secure the patient interface in place and the mask may be adjusted to apply sufficient pressure to provide the desired seal with the patient. Neither the headgear nor the mask needs to be over tightened or under tightened to accommodate the requirements of the other feature.
Although such a device has certainly advanced the art, even this design could still be further improved upon. For instance, this device separates the headgear retention forces from the mask seal forces. Yet, this mask still concentrates the headgear strapping forces along the straps rather than dispersing it about the patient's head. In addition, the headgear assembly, as in the prior references, circumnavigates the patient's head about a curved path that results in squeezing inwardly on the patient's head as the headgear assembly is tightened. An additional feature of this invention that could be further improved is that the straps can creep together resulting in the patient interface becoming misaligned during use. Creep of the straps can potentially undermine the seal between the patient interface and the patient or cause the patient discomfort.
Accordingly, it would be desirable to have a patient interface with a headgear assembly that is capable of maximizing patient comfort. It would also be desirable to have a patient interface with a headgear assembly that is better able to resist misalignment. It would be further desirable to have a system that has a patient interface and headgear assembly wherein each structure is secured to the patient with the optimum force needed to achieve their separate functions. It would be still further desirable to have a headgear assembly that can be secured to the patient's head without applying a continuous force about the patient's head and thereby squeezes the sides of the patient's head inwardly. It would be still yet further desirable to have a headgear assembly that disperses the forces necessary to retain the headgear on the patient's head.